Generally, a washing machine has a drum equipped therein and washes laundry by rotating the drum. In this washing machine, there is also installed a tub for accommodating the drum, preliminarily storing washing water and feeding the stored washing water to the drum. The tub is connected with an inlet pipe, and the inlet pipe is connected with a detergent box so as to feed the detergent along the washing water to the tub.
However, the bubbles generated by the detergent during a washing are introduced into the detergent box through the inlet pipe to contaminate the detergent box. Further, the bubbles may be leaked to the outside through the detergent box and may contaminate the washing machine and the surrounding thereof.
In particular, compared with the top loading type of washing machine in which the drum and the tub stand, the front loading type of washing machine causes more serious bubble generation, so that the leakage possibility of the generated bubbles increases. To this end, in the front loading type of washing machine, it is requested that the detergent particularly generating a small amount of bubbles be used. However, the use of such a detergent does not exclude the leakage possibility of the bubbles  completely.